- From: Seaborne, Andy <andy.seaborne@hp.com>
- Date: Thu, 17 Mar 2005 12:58:24 +0000
- To: "Thompson, Bryan B." <BRYAN.B.THOMPSON@saic.com>
- Cc: "'public-rdf-dawg@w3.org'" <public-rdf-dawg@w3.org>
Thompson, Bryan B. wrote: > Hello, > > I am trying to figure out what semantic constraints are present on the > QuotedURI(Ref) for the BaseDecl and PrefixDecl productions. > > Are the QuotedURIRefs for BaseDecl and/or PrefixDecl _required_ to be > absolute URIs? May they be relative URIs? Opaque? Standard relative URI resolution applies. > > Are there any constraints on the kind of URI that may be used for a > BaseDecl? E.g., a URN? URIs. Standard rules, including the RDF rule for qname-like-thing to URI by concatenation. > > Should the BaseDecl be used to resolve a relative URI in a PrefixDecl? Yes. BASE must be first. There was some text about this but it seems to have gone away. Strange. > > The spec says that a PrefixDecl may be re-bound. However, I can not > think of any use case for this. Since prefixes may only be bound at > the top of the query, and since a PrefixDecl may not use a QNAME, it > seems likely that re-defining a prefix will always indicate a user > error. Possibly an error - possibly filling in a template. It was a WG decision from a while ago. Whatever Turtle or N3 does. > > Is there any default namespace if none has been defined? If not, is > it an error to write ":foo" if the default namespace has not been > bound? There isn't a notion of default namespace - just the namespace with prefix "" which is spoken of as the default namespace but technically it isn't. ":foo" is legal only if "PREFIX : <...>" has been used. It does not default. Common usages in N3/Turtle include: @prefix : <> . @prefix : <#> . but they are less useful in s SPARQL query unless you use BASE as well (or external equivalent). Hmm - there is a bug in the grammar at the moment in that <> is not allowed - it should be. RFC 3896, sec 4.2 has the rules. I would prefer not to reproduce 3896 in this doc and assume there is an external URI parser/checker/resolver. A comment in the grammar should suffice. > > Thanks, > > -bryan > Andy
Received on Thursday, 17 March 2005 12:58:54 UTC